The Centre proposes to deploy four Cutter Suction Dredgers (CSD) and a Hydraulic Surface Dredger (HSD) on Brahmaputra river in addition to the ones currently operating. Four more CSD and one HSD units are under construction for deployment in the Brahmaputra River National Waterway, said Union Minister for Shipping, TR Baalu. Replying to a question by Rajen Gohain, Baalu said for maintaining the channel for shipping and navigation, dredging is being carried out during low water season at shallow patches, according to requirement and availability of dredgers. The 891 km route from Sadiya to Dhubri was declared a national waterway in 1988.